Podcast
Questions and Answers
Toxicology is defined as the study on harmful effects of toxins.
Toxicology is defined as the study on harmful effects of toxins.
True
Immunoassay is primarily used for confirming drug test results.
Immunoassay is primarily used for confirming drug test results.
False
In clinical toxicology, patient consent is not required before testing.
In clinical toxicology, patient consent is not required before testing.
True
Gas chromatography and mass spectrometry are considered a gold standard in toxicological analysis.
Gas chromatography and mass spectrometry are considered a gold standard in toxicological analysis.
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All screening results from forensic toxicology can be used for medical evaluation.
All screening results from forensic toxicology can be used for medical evaluation.
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Some NSAID drugs can give false positive reactions in immunoassay tests.
Some NSAID drugs can give false positive reactions in immunoassay tests.
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Identity of specimen in forensic toxicology is presumed without proof.
Identity of specimen in forensic toxicology is presumed without proof.
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The sensitivity of immunoassay allows for the detection of large amounts of drugs only.
The sensitivity of immunoassay allows for the detection of large amounts of drugs only.
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Gas Chromatography is a method that does not alter the chromatographic characteristics of the substance being analyzed.
Gas Chromatography is a method that does not alter the chromatographic characteristics of the substance being analyzed.
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High Performance Liquid Chromatography is suitable for analyzing substances that are heat-labile.
High Performance Liquid Chromatography is suitable for analyzing substances that are heat-labile.
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Gas Chromatography typically has a slower process compared to High Performance Liquid Chromatography.
Gas Chromatography typically has a slower process compared to High Performance Liquid Chromatography.
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High Performance Liquid Chromatography utilizes a gas as the mobile phase.
High Performance Liquid Chromatography utilizes a gas as the mobile phase.
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Mass Spectrometry sorts ions based on their mass-to-charge ratio after ionizing chemical samples.
Mass Spectrometry sorts ions based on their mass-to-charge ratio after ionizing chemical samples.
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False positives can occur due to the presence of interfering substances or cross-reactions with reagents.
False positives can occur due to the presence of interfering substances or cross-reactions with reagents.
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The 'gold standard' for drug detection is a combination of High Performance Liquid Chromatography and Mass Spectrometry.
The 'gold standard' for drug detection is a combination of High Performance Liquid Chromatography and Mass Spectrometry.
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One of the missions related to poisoning incidents is to promote research and documentation of poisoning cases.
One of the missions related to poisoning incidents is to promote research and documentation of poisoning cases.
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Study Notes
Toxicological Aspects of Substance Abuse
- Toxicology is the study of harmful effects of toxins. It has clinical and forensic applications.
- Clinical toxicology focuses on emergency screening (e.g., overdose), toxic exposure, and therapeutic drug monitoring (TDM).
- Forensic toxicology involves postmortem analysis, criminal investigations, workplace drug testing, and sports drug testing.
Key Differences Between Clinical and Forensic Toxicology
| Feature | Clinical | Forensic |
|---|---|---|
| Consent | Not required | Required |
| Specimen ID | Presumed | Must be proven |
| Results used for | Medical evaluation | Legal action |
| Screening results | Sufficient for medical decisions | Only confirmed positive results are considered |
Analytical Problems in Toxicology
- Endogenous substances (e.g., cholesterol, fats, proteins, putrefactive amines) can interfere with analyses.
- A wide range of drug concentrations exist, varying greatly. (Therapeutic concentrations range over at least 100,000 fold). Some variation can even exceed 1000 times.
- Some drugs are difficult to detect due to the analytical conditions or can be very unusual.
Analytical Basis of Toxicology
- Immunoassay: Used for preliminary screening; antibody-antigen reaction detects small amounts of drug/metabolites. ELISA and RIA are examples of immunoassays.
Immunoassay Principles
- Low levels of the target protein yield a weaker signal than high levels in immunoassays.
- Sample preparation steps result in measurement of antigen levels by the concentration observed.
- Antibodies bind to the antigens and then an enzyme converts a substrate to a measurable signal.
- The higher the absorbance, the higher the concentration of the analyte.
Disadvantages of Immunoassay
- Specificity issues: Some substances can cross-react and generate false-positive results (e.g., cannabinoid detection, NSAID drugs, codeine, and antihistamines can produce false positives from cross-reactions).
- Good for screening but not confirmation.
Chromatography
- Aims to separate components of a mixture based on their affinity differences between mobile and stationary phases.
- Gas chromatography (GC) coupled with mass spectrometry (MS) is a common technique. Typically, a rapid immunoassay is conducted beforehand to reduce the sample size by eliminating the negatives before GC/MS analysis.
- High-performance liquid chromatography (HPLC) is used when the compound is not volatile or is heat-labile. HPLC/MS is used for such compounds.
Gas Chromatography (GC)
- Uses heat to vaporize the sample (destructive process).
- GC/MS is combined to physically separate (purify) the compound and then fingerprint the drug/chemical for identification
- GC/MS is considered a gold standard.
High-Performance Liquid Chromatography (HPLC)
- Used for non-volatile or heat-labile substances, such as steroids or benzodiazepines.
GC vs HPLC for Drug Detection
| Feature | GC | HPLC |
|---|---|---|
| Sample Destruction | Destroys or burns sample | Doesn't destroy sample |
| Mobile Phase | Gas | Liquid |
| Sampling | Large | Lower |
| Specificity | High | High |
| Speed | Faster | Slower |
Mass Spectrometry (MS)
- Ionizes chemical samples and sorts ions based on their mass-to-charge ratio.
Cocaine
- Chemical formula: C₁₇H₂₁NO₄
- Molecular weight (MW): 303.35
Cocaine Fragmentation (EI)
- EI fragmentation breaks down the cocaine molecule producing characteristic fragment ions.
Cocaine Mass Spectrum
- Shows relative abundance of fragments according to their mass-to-charge ratio (m/z).
- Note: The 82 ion is the base peak and is prominent, along with ions relating to the loss from 303 (M+).
Amphetamine Fragmentation
- Fragmentation pathways for amphetamine molecules into their constituent ions.
Amphetamine Mass Spectrum
- A mass spectrum displaying the relative abundance of fragments according to the mass-to-charge ratio (m/z) of amphetamine. Characteristic peaks represent fragments formed by the breakdown of the amphetamine molecule.
Interpretation of Test Results
- False negatives: Occurs when drug is present but not detected (due to threshold too high, low quantity).
- False positives: Interfering substances in the biological fluid cross-react with the reagents (e.g., OTC medications, herbal teas).
Mission of National Poison Centre
- Reduce mortality, morbidity, cost, and occurrence of poisoning through excellence, compassion, and innovation.
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Description
Explore the critical distinctions between clinical and forensic toxicology in this quiz. Delve into topics like emergency screening in clinical settings and the legal implications of forensic toxicology. Understand the applications in both fields and the importance of consent and specimen identification.
